'Golden Teacup' refers to a situation where you are having anal intercourse with your partner. At some point during the situation, if you decide to pee in your partner's butthole, you will have given your partner a 'Golden Teacup.' This can also refer to accidentally peeing in your partner's butthole. Girls can also give a 'Golden Teacup' as a perverse version of a 'Golden Shower.'

Heybaby, I want to bend you over and give you a golden teacup; I haven't drank water all day and my urine will be neon!